Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 241200
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
700 AM CDT Tue Apr 24 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 332 AM CDT Tue Apr 24 2018

Regional IR satellite continues to show clouds wrapping around the
pesky upper level system we have been dealing with the last couple
of days. Surface analysis depicts a stark divide in the moist
surface layer that extends as far west as Eastern Missouri. Much
drier air lies just a bit further west across Central Missouri,
where clouds cleared yesterday and allowed temperatures to rebound
into the 60s and 70s.

Low level moisture will hang on just bit longer along the
Mississippi and eastward. There will be the potential for a few
showers and patchy fog through the early morning, but chances for
rain diminish with the ever-so-slow eastward trend in the dry air
and decreasing cloud cover early this afternoon. Forecast soundings
suggest we could see another day with a fairly sharp divide with low
clouds and higher RH hanging on to eastern counties of the forecast
area. Those further west will see improvement with sunshine possible
across southwest IL by mid to late afternoon. Where sun does appear,
we could get better mixing, resulting in some gusty winds.

High pressure builds from the north and west through Tuesday night.
Mid level clouds will linger and begin to thicken again late in the
period ahead of the next system. Chances for precip should hold off
until the very tail end of the period. Even then, only the western
fringes of the forecast area run a slight chance of POPs.

Maples

.LONG TERM...  (Wednesday through Monday)
Issued at 332 AM CDT Tue Apr 24 2018

The synoptic pattern at the start of the long term period will
feature a fairly active northwest flow regime which will allow for a
couple PV anomalies to slide through the region and reinforce an
eastern CONUS trough. However, by the end of the week into this
upcoming weekend mid-level heights will finally begin to rise as a
ridge builds into the central CONUS. This ridging aloft will bring a
highly anticipated warmup to the area this weekend and into early
next week.

A fairly strong but compact PV anomaly will be across portions of
the central Plains Wednesday morning. It will quickly dive southeast
into the southeastern CONUS by Thursday morning. It appears this
track will keep the bulk of the large-scale ascent to the southwest
of the area. Additionally, this track will enable a fairly dry low-
level airmass to remain locked in place over the region. The end
result of these two factors is that much of the region will remain
dry, although a few showers may clip portions of central and
southeast MO on Wednesday as the system passes through.

Quick on its heels will be another trough which will plow through
the area Thursday night into Friday. Guidance differs a bit with the
strength of this system, with the Euro suggesting more of a split
trough whereas the GFS is stronger and more phased. The GEM and the
other ensemble data tend to suggest the GFS is likely an outlier,
thus have favored a weaker solution and have gone with mainly slight
chance pops with this passing trough and associated surface cold
front Thursday night into Friday.

A fairly significant pattern shift then looks to take place by next
weekend as a trough builds into the southwestern CONUS and ridging
takes hold over the Plains and Midwest. As surface ridging slides
off to the east, winds will turn to the southwest and the warmup
will commence especially Sunday into Monday. After highs in the 60s
for the rest of this week, they will push into the 70s this weekend
and perhaps even into the lower 80s by early next week. It appears
the operational GFS and the operational Euro high temperatures are
both on the higher side of their ensembles, so will not get too
carried away on raising temperatures for Sunday into early next week
at this point in time.

Deitsch

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 640 AM CDT Tue Apr 24 2018

A range cigs/vsbys exist across the region, from LIFR in Central
Illinois to VFR in Central Missouri. Expect gradual improvement
from west to east through the day. Most IFR should erode from 12z
to 18z as areas of fog diminish with a few showers possible,
mainly east of the Mississippi River. Drier air will work in from
the west with OVC cigs eventually breaking and lifting at or
above MVFR by 18z. Locations that clear out sooner could gust to
20 kts with deeper mixing through the afternoon. Expected VFR
conditions through tonight with a few mid to high clouds.

SPECIFICS FOR KSTL:
IFR cigs will hold through the early morning hours with vsbys in
the 4-5SM range until mid-morning. A brief, light shower is
possible, but most activity should remain to the east. The upper
low responsible for the clouds will continue to depart the region
with drier air gradually working in from the west. This will
result in cigs/vsbys lifting to MVFR through the morning and VFR
by early afternoon. Winds could gust near 20 kts out of the north
as skies break. VFR conditions are then expected to hold through
tonight and into Wednesday morning.


Maples

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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